1. Field of the Invention
The invention relates to electrical switching apparatus, such as, for example, circuit breakers and, more particularly, to circuit breakers including a slot motor.
2. Background Information
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. Circuit breakers include at least one pair of separable contacts. A first contact is fixed within the circuit breaker housing and a second movable contact is coupled to an operating mechanism. These separable contacts are in electrical communication with either the line or the load coupled to the circuit breaker. The operating mechanism moves the movable contact between a first, open position wherein the movable contact is spaced from the fixed contact, and a second, closed position wherein the fixed and movable contacts are in contact and in electrical communication. The operating mechanism may be operated manually or by a trip mechanism.
In order to enhance the speed of separation of the separable contacts, the contacts may be disposed within a slot motor, which increases interruption performance. The slot motor is a ring-shaped, loop-shaped or U-shaped device made of magnetically permeable material (e.g., steel), which at least generally surrounds the separable contacts and a movable contact arm of the operating mechanism. When the circuit is live, an electrical arc may be drawn between the contacts during separation. The electrical current interacts electromagnetically with the slot motor to induce a magnetic field in the magnetic material of the slot motor, which, in turns, interacts with the separating contacts and the movable contact arm to accelerate the contact opening process. Examples of slot motors are disclosed in U.S. Pat. Nos. 4,375,021; 4,546,336; 4,546,337; 4,549,153; 4,970,482; 5,694,098, and 6,281,459.
Ring-shaped or loop-shaped slot motors typically have two assemblies, an upper assembly and a lower assembly. Both upper and lower assemblies include a corresponding housing and a plurality of plates composed of the magnetically permeable material. The lower assembly is disposed below the fixed contact.
Upon interruption of a short circuit or other fault condition by a circuit breaker, molten metal may be deposited throughout the internals of the circuit breaker, which may impair its performance.
Hence, there is room for improvement in electrical switching apparatus, such as circuit breakers, and in components therefor.